首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8665篇
  免费   747篇
  国内免费   170篇
系统科学   1183篇
丛书文集   95篇
教育与普及   70篇
理论与方法论   288篇
现状及发展   876篇
研究方法   13篇
综合类   7057篇
  2024年   16篇
  2023年   45篇
  2022年   59篇
  2021年   55篇
  2020年   42篇
  2019年   21篇
  2018年   743篇
  2017年   751篇
  2016年   453篇
  2015年   93篇
  2014年   102篇
  2013年   78篇
  2012年   354篇
  2011年   1028篇
  2010年   931篇
  2009年   560篇
  2008年   640篇
  2007年   901篇
  2006年   120篇
  2005年   151篇
  2004年   227篇
  2003年   255篇
  2002年   175篇
  2001年   127篇
  2000年   109篇
  1999年   174篇
  1998年   176篇
  1997年   182篇
  1996年   169篇
  1995年   153篇
  1994年   132篇
  1993年   96篇
  1992年   86篇
  1991年   118篇
  1990年   68篇
  1989年   67篇
  1988年   48篇
  1987年   41篇
  1986年   19篇
  1985年   11篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1967年   1篇
排序方式: 共有9582条查询结果,搜索用时 109 毫秒
791.
This report presents experimental observations of dramatic variations in STM images of bis [1,3-DI(p-n-tetradecyloxyphenyl)propane-1,3-dionato]copper( Ⅱ) (abbreviated to C14O-Cu)physisorbed on HOPG as the bias voltage is changed .Several representative image patterns were obtained for the rich changes of the internal contrast of the molecule .Submolecular features of the molecular cores and the interdigitated alkyl parts are clearly visible.  相似文献   
792.
An important precursor 4,5-didodecylthiolphthalonitrile (DCP) for synthesis of phthalocyanines (Pcs) and subphthalocyanines (SubPcs) was synthesized and the assembling structure of this molecule on the basal plane of highly oriented pyrolytic graphite (HOPG) surface was characterized using the scanning tunneling microscopy (STM) in ambient conditions. In high-resolution images of the molecules, we found that the arrangement of the cyano groups forms a “head-to-head” configuration to keep the stability of the entire system. The mismatch of the DCP molecules with the substrate lattice has also been observed in the experiment.  相似文献   
793.
Universe, ecosystem, social system, etc. are evolving systems. The evolving processes of thesesystems have gradual small changes and rapid drastic changes with uncertainties under the constraintsof environment. Systems, as a whole, are evolving toward complexity, diversity and variety withfluctuations and jumps. New order emerges from "mutations". The evolution is bothchance-dependent and path-dependent. In this paper three basics: entropy, information and noise areemphasized with regard to system evolution which is a field that can give people wisdom to solvesystem problems with domain knowledge.  相似文献   
794.
以求解Burger‘s方程的中心差分格式,显示逆风格式,Samarskii格式及修正Dennis格式为基础,构造了若干新的AGE方法,讨论了方法的线性化稳定性数值结果表明,对于求解Burger’s方程大Reynold数问题,除了C-AGE方法外,文中所构造的其他AGE方法明显优于Evans的分组显式方法。  相似文献   
795.
This study evaluates performance of information criteria used to separate latent classes. In the evaluations, various numbers of latent classes, sample sizes, parameter structures and latent-class complexities were designed to simulate datasets. The average accuracy rates of information criteria in selecting the designed numbers of latent classes were the core results in this experiment. The study revealed that widely used information criteria, e.g., AIC, BIC, CAIC, could perform poorly under some circumstances. By including a sample size adjustment (Rissanen, 1978), the unsatis-factory performances could be improved considerably. The sample size adjustment provides a plausible solution for separating latent classes. Guidelines are provided to help achieve optimum use of the model fit indices.  相似文献   
796.
In the era of e-businesses, the traditional business services are greatly challenged by the ever-increasing demands from customers with various backgrounds and personalities. Large numbers of new e-businesses are driven by the needs of customers. The existing dynamics inherent in the customer needs require the corresponding dynamic management of services. Attempting to respond to customers in a rapid and intelligent way, this paper proposes a situation calculus based approach for dynamically managing e-Business services in the ubiquitous environment. By employing the formalism of the situation calculus to enable intelligence and automation, the approach can implement. the functions of service automatic composition and model verification. These functions will improve the degree of customer-orientation and enable fast responsiveness in the emerging e-service systems.  相似文献   
797.
Formal systems engineering approaches to modeling misperceptions and attitudes are employed within the framework of the graph model for conflict resolution to systematically study the War of 1812 between the United States of America and Great Britain in order to provide enhanced insights into the causes of the war. More specifically, relational definitions for preferences, movements and stability concepts are defined for describing the attitudes and associated behavior of decision makers involved in a conflict. To capture misperceptions of decision makers in the War of 1812, attitudes are studied within the structure of a hypergame. Combining attitudes and misperceptions within the paradigm of the graph model furnishes the flexible analytical tool which demonstrates that misunderstanding of attitudes by Great Britain and the United States may have contributed to the outbreak of this nasty war.  相似文献   
798.
Polynomial composition is the operation of replacing variables in a polynomial with other polynomials. λ-Grgbner basis is an especial Grobner basis. The main problem in the paper is: when does composition commute with λ-Grobner basis computation? We shall answer better the above question. This has a natural application in the computation of λ-Grobner bases.  相似文献   
799.
在校大学生消费情况分析及科学理财模式的构筑   总被引:1,自引:0,他引:1  
通过问卷调查对在校大学生的消费结构现状进行了分析,指出目前大学生消费结构中存在的问题,提出从社会、家庭、学校、学生个人四个方面全方位构筑大学生科学的理财模式,以期对大学生合理消费模式的形成提供指导.  相似文献   
800.
Company bankruptcies cost billions of dollars in losses to banks each year. Thus credit risk prediction is a critical part of a bank's loan approval decision process. Traditional financial models for credit risk prediction are no longer adequate for describing today's complex relationship between the financial health and potential bankruptcy of a company. In this work, a multiple classifier system (embedded in a multiple intelligent agent system) is proposed to predict the financial health of a company. In our model, each individual agent (classifier) makes a prediction on the likelihood of credit risk based on only partial information of the company. Each of the agents is an expert, but has limited knowledge (represented by features) about the company. The decisions of all agents are combined together to form a final credit risk prediction. Experiments show that our model out-performs other existing methods using the benchmarking Compustat American Corporations dataset.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号